Sketch the graph of the polynomial function $$ p(x) = 2x^4+9x^3+7x^2+8x $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ 2x^4+9x^3+7x^2+8x = 0 } $

The solutions of this equation are:

$$ \begin{matrix}x_1 = 0 & x_2 = -3.8619 \end{matrix} $$

(you can use the step-by-step polynomial equation solver to see a detailed explanation of how to solve the equation)

STEP 2:Find the y-intercepts

To find the y-intercepts, substitute $ x = 0 $ into $ \color{blue}{ p(x) = 2x^4+9x^3+7x^2+8x } $, so:

$$ \text{Y inercept} = p(0) = 0 $$

STEP 3:Find the end behavior

The end behavior of a polynomial is the same as the end behavior of a leading term.

$$ \lim_{x \to -\infty} \left( 2x^4+9x^3+7x^2+8x \right) = \lim_{x \to -\infty} 2x^4 = \color{blue}{ \infty } $$

The graph starts in the upper-left corner.

$$ \lim_{x \to \infty} \left( 2x^4+9x^3+7x^2+8x \right) = \lim_{x \to \infty} 2x^4 = \color{blue}{ \infty } $$

The graph ends in the upper-right corner.

STEP 4:Find the turning points

To determine the turning point, we need to find the first derivative of $ p(x) $:

$$ p^{\prime} (x) = 8x^3+27x^2+14x+8 $$

The x coordinate of the turning point is located at the zeros of the first derivative

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x = -2.8891 \end{matrix} $$

(cleck here to see a explanation of how to solve the equation)

To find the y coordinate, substitute the above value into $ p(x) $

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ -2.8891 } \Rightarrow p\left(-2.8891\right) = \color{orangered}{ -42.3783 }\end{aligned} $$

So the turning point is:

$$ \begin{matrix} \left( -2.8891, -42.3783 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 24x^2+54x+14 $.

The zeros of second derivative are

$$ \begin{matrix}x_1 = -0.299 & x_2 = -1.951 \end{matrix} $$

Substitute the x values into $ p(x) $ to get y coordinates

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ -0.299 } \Rightarrow p\left(-0.299\right) = \color{orangered}{ -1.9907 }\\[1 em] \text{for } ~ x & = \color{blue}{ -1.951 } \Rightarrow p\left(-1.951\right) = \color{orangered}{ -26.8226 }\end{aligned} $$

So the inflection points are:

$$ \begin{matrix} \left( -0.299, -1.9907 \right) & \left( -1.951, -26.8226 \right)\end{matrix} $$

Graphing Polynomials